Magnetic device and magnetic sensor using the same

ABSTRACT

A magnetic sensor has a three-terminal magnetic device consisting of an emitter, a base, and a collector. A semiconductor layer serving as the collector and a magnetic multilayered film serving as the base form a Schottky junction. The magnetic multilayered film has two magnetic films opposing each other with a nonmagnetic film between them. The emitter constructed of a metal film and the base are connected via a tunnel insulating film. The relationship between the magnetization directions in the magnetic films changes in accordance with an external magnetic field, and this changes the value of a current flowing through the magnetic device. The external magnetic field is sensed on the basis of this change in the current value.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a magnetic device used as, e.g., amagnetic field sensing device for sensing a very weak magnetic field ina very small region, and a magnetic sensor using the same.

2. Description of the Related Art

Increases in the density and speed of magnetic recording largely dependupon the improvement of magnetic recording media and the progress ofmagnetic recording apparatuses, particularly the progress of magneticheads for performing write and read operations in magnetic recording.For example, with the decreasing sizes and the increasing capacities ofthe recent magnetic recording media, a relative speed between a magneticrecording medium and a read magnetic head is decreased. Accordingly, asa new type of a read magnetic head capable of extracting a high outputeven at a low relative speed, a magnetic head called a magnetoresistanceeffect head (to be referred to as an MR head hereinafter), particularlya giant magnetoresistance effect head (to be referred to as a GMR headhereinafter) has drawn attention. The GMR head uses a largemagnetoresistance effect of a multilayered film consisting of a magneticmaterial and a nonmagnetic material. Various kinds of the GMR heads havebeen proposed, and a GMR head of type called a spin valve head isconsidered to be promising among them all.

This spin valve GMR head has a basic structure in which a ferromagneticlayer, a nonmagnetic layer, and a ferromagnetic layer are stacked on anantiferromagnetic layer. The direction of magnetization in the lowerferromagnetic layer is spatially fixed by an exchange interaction actingbetween this ferromagnetic layer and the antiferromagnetic layer. Themagnetization in the upper ferromagnetic layer weakly interacts with themagnetization in the lower ferromagnetic layer through the nonmagneticlayer. However, the upper ferromagnetic layer can beantiferromagnetically coupled with the lower ferromagnetic layer byproperly selecting the thickness of the nonmagnetic layer. That is, whenan external magnetic field is zero, the magnetization in the upperferromagnetic layer couples with the magnetization in the lowerferromagnetic layer in opposite directions. Since this antiferromagneticmagnetic coupling is weak, the direction of the magnetization in theupper ferromagnetic layer is readily reversed if an external magneticfield is applied to the direction of the magnetization in the lowerferromagnetic layer. That is, under an external magnetic field, thedirections of magnetization in the upper and the lower ferromagneticlayers are the same.

It is known that the electric resistance of a multilayered filmconsisting of a ferromagnetic layer/nonmagnetic layer/ferromagneticlayer structure depends upon the relative magnetization direction in theupper and the lower ferromagnetic layers. This is so because in amagnetic material the scattering of conduction electrons depends uponthe spin magnetic moments of the electrons. Since the relativemagnetization direction in the multilayered film described above dependsupon an external magnetic field, the electric resistance of the filmstrongly depends upon the external magnetic field. This phenomenon iscalled a giant magnetoresistance effect. The spin valve GMR head usesthis giant magnetoresistance effect and reads out magnetically recordeddata.

Although the magnetic head using the giant magnetoresistance effect hasexcellent characteristics, it also has several drawbacks. The main causeof these drawbacks is that the multilayered film having the giantmagnetoresistance effect is a metal multilayered film with a lowelectric resistance, and so it is necessary to increase the density of acurrent made to flow through the multilayered film in order to obtain asufficient output voltage. When the density of a current made to flowthrough the device is thus increased, the device generates heat,electromigration occurs, or a magnetic field is generated by thecurrent, thereby making the device operation unstable.

A larger magnetoresistance effect is expected when a current is made toflow vertically in the multilayered film. However, since the absolutevalue of the resistance is very small in this direction, no practicaldevice can be obtained from the present GMR head structure.

As described above, in the conventional magnetic heads using themagnetoresistance effect, the density of a current made to flow throughthe multilayered film must be increased to obtain a sufficient outputvoltage. When the current density is thus increased, the devicegenerates heat, electromigration occurs, or a magnetic field isgenerated. It is therefore necessary to eliminate these problems. Also,a magnetic head structure is demanded in which a sufficient outputvoltage can be obtained with a low current density even when a currentis made to flow vertically in the multilayered film, in which case alarger magnetoresistance effect can be expected.

SUMMARY OF THE INVENTION

The present invention has been made in consideration of the abovesituation, and has as its object to provide a magnetic device whichoperates well with a low current density and has a high sensitivity, anda magnetic sensor using the same.

A magnetic device according to a first aspect of the present inventioncomprises:

a multilayered film including first and second magnetic films and anonmagnetic film interposed between the first and second magnetic films;

an electron collecting section including a semiconductor layer connectedto one surface of the multilayered film via a Schottky junction; and

an electron injecting section including a metal film connected to theother surface of the multilayered film via a tunnel junction member.

A magnetic device according to a second aspect of the present inventioncomprises:

a multilayered film having a first magnetic film and a nonmagnetic film;

an electron collecting section including a semiconductor layer connectedto the first magnetic film via a Schottky junction; and

an electron injecting section including a second magnetic film connectedto the nonmagnetic film via a tunnel junction member.

A magnetic device according to a third aspect of the present inventionis a device according to the first or second aspect, wherein the firstand second magnetic films are so set as to have different coerciveforces.

A magnetic device according to a fourth aspect of the present inventionis a device according to any one of the first to third aspects, whereinthe tunnel junction member comprises a resonant tunnel structureincluding first and second barrier layers and a quantum well layerinterposed between the first and second barrier layers.

A magnetic device according to a fifth aspect of the present inventioncomprises:

a tunnel junction member having a resonant tunnel structure includingfirst and second barrier layers and a quantum well layer interposedbetween the first and second barrier layers and consisting of a firstmagnetic film;

an electron collecting section connected to one surface of the tunneljunction member; and

an electron injecting section connected to the other surface of thetunnel junction member, the electron injecting section including asecond magnetic film having a coercive force lower than a coercive forceof the first magnetic film.

A magnetic device according to a sixth aspect of the present inventionis a device according to the fifth aspect, wherein the electroncollecting section includes a semiconductor layer connected to thetunnel junction member via a Schottky junction.

A magnetic device according to a seventh aspect of the present inventionis a device according to the sixth aspect, wherein the tunnel junctionmember includes a third magnetic film which forms the Schottky junctiontogether with the semiconductor layer, and the third magnetic film hassubstantially the same coercive force as the coercive force of thesecond magnetic film.

A magnetic device according to an eighth aspect of the present inventionis a device according to the fifth aspect, wherein the electroncollecting section includes a third magnetic film, and the thirdmagnetic film has substantially the same coercive force as the coerciveforce of the second magnetic film.

A magnetic sensor according to a ninth aspect of the present inventioncomprises:

a magnetic device according to any one of the first to eighth aspects;

a power supply for applying a voltage to the electron injecting section;and

means for detecting a current flowing out from the electron collectingsection, wherein when a relationship between magnetization directions inthe first and second magnetic films is changed by an external magneticfield, the current flowing out from the electron collecting sectionchanges accordingly, and the external magnetic field is sensed on thebasis of the change in the current.

The magnetic device of the present invention uses the spin scattering ofelectrons vertically flowing through the magnetic film or themultilayered film consisting of the magnetic film and the nonmagneticfilm. Accordingly, a high sensitivity can be obtained in principle.Also, an applied voltage is supported by a tunnel junction or a Schottkyjunction, and a Schottky barrier has a high junction resistance.Therefore, an appropriate current value can be easily obtained under adesired bias voltage.

Additional objects and advantages of the invention will be set forth inthe description which follows, and in part will be obvious from thedescription, or may be learned by practice of the invention. The objectsand advantages of the invention may be realized and obtained by means ofthe instrumentalities and combinations particularly pointed out in theappended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute apart of the specification, illustrate presently preferred embodiments ofthe invention and, together with the general description given above andthe detailed description of the preferred embodiments given below, serveto explain the principles of the invention.

FIGS. 1A to 1C are views for explaining the principle of a magneticdevice and a magnetic sensor using the device according to the presentinvention;

FIGS. 2A and 2B are views showing a device in which a nonmagnetic filmis connected via a tunnel barrier and a semiconductor film is connectedvia a Schottky junction, to the multilayered film shown in FIG. 1A;

FIG. 3 is a graph showing the state density of electrons in Fe;

FIG. 4 is a graph showing the state density of electrons in Co;

FIG. 5 is a view conceptually showing a magnetic device according to anembodiment of the present invention;

FIG. 6 is a sectional view showing a practical structure of the magneticdevice shown in FIG. 5;

FIG. 7 is a view showing a state density of electrons depending uponspins in a ferromagnetic material;

FIG. 8 is a graph showing the tunnel characteristic between the emitterand the base of a magnetic device of Example 1;

FIG. 9 is a graph showing the Schottky characteristic between the baseand the collector of the magnetic device of Example 1;

FIG. 10 is a graph showing the emitter-base voltage dependence of acollector current in the magnetic device of Example 1;

FIG. 11 is a graph showing the magnetic field response of the collectorcurrent in the magnetic device of Example 1;

FIG. 12 is a view conceptually showing a magnetic device according toanother embodiment of the present invention;

FIG. 13 is a view conceptually showing a magnetic device according tostill another embodiment of the present invention;

FIG. 14 is a view conceptually showing a magnetic device according tostill another embodiment of the present invention;

FIG. 15 is a view conceptually showing a magnetic device according tostill another embodiment of the present invention;

FIG. 16 is a view conceptually showing a magnetic device according tostill another embodiment of the present invention;

FIG. 17 is a view conceptually showing a magnetic device according tostill another embodiment of the present invention;

FIG. 18 is a sectional view showing a practical structure of themagnetic device shown in FIG. 14;

FIG. 19 is a graph showing the magnetic field response of a collectorcurrent in a magnetic material device of Example 2;

FIG. 20 is a graph showing the energy band of a double barrier resonanttunnel device using a semiconductor heterojunction;

FIG. 21 is a graph showing the current-voltage characteristic of theresonant tunnel device shown in FIG. 20;

FIG. 22 is a view conceptually showing a magnetic device according tostill another embodiment of the present invention, in which a resonanttunnel junction member is used in the magnetic device shown in FIG. 5;

FIG. 23 is a view conceptually showing a magnetic device according tostill another embodiment of the present invention; and

FIG. 24 is a view conceptually showing a magnetic device according tostill another embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The principle of a magnetic device and a magnetic sensor using the sameaccording to the present invention will be described below withreference to FIGS. 1A to 4.

In a magnetic material, a state density of electrons splits between anup-spin band and a down-spin band. For example, as shown in FIG. 1A,assume that in a multilayered film MLF consisting of a magnetic film F1,a nonmagnetic film N1, and a magnetic film F2, magnetization directionsMD1 and MD2 in the magnetic films F1 and F2 are opposite to each other.In this structure, as shown in FIGS. 1B and 1C, the state densities ofelectrons in the magnetic films F1 and F2 have opposite characteristicsfor up-spin electrons (indicated by upward arrows) and down-spinelectrons (indicated by downward arrows).

FIG. 2A shows a device in which a nonmagnetic film N2 is connected tothe magnetic film F1 of the multilayered film MLF via a tunnel barrierTB and a semiconductor film SEM made of, e.g., silicon, forms a Schottkyjunction with the magnetic film F2. In this device, when a voltage isapplied between the nonmagnetic film N2 and the multilayered film MLF sothat the nonmagnetic film N2 becomes negative, the nonmagnetic film N2generates electrons (hot electrons) having energy EN higher than a Fermilevel E_(F) of the magnetic films F1 and F2.

Assume, as shown in FIG. 2A, that the magnetization directions MD1 andMD2 in the magnetic films F1 and F2 remain opposite (antiparallel) toeach other. If this is the case, the state density of electrons in themagnetic film F1 at the energy EN is high for the down-spin electronsand substantially zero for the up-spin electrons. As a consequence, onlythe down-spin electrons move from the nonmagnetic film N2 and reach themagnetic film F1 through the tunnel barrier TB. However, the statedensity of electrons in the magnetic film F2 at the energy EN issubstantially zero for the down-spin electrons. Accordingly, thedown-spin electrons passing through the tunnel barrier TB are reflectedby the magnetic film F2, i.e., they cannot move from the magnetic filmF1 to the magnetic film F2.

Assume, as illustrated in FIG. 2B, that the magnetization direction inthe magnetic film F2 is changed by an external magnetic field andconsequently the magnetization directions MD1 and MD2 in the magneticfilms F1 and F2 become the same (parallel). In this case, the statedensities of electrons in both the magnetic films F1 and F2 at theenergy EN are high for the down-spin electrons and substantially zerofor the up-spin electrons. Consequently, only the down-spin electronsmove from the nonmagnetic film N2 to the magnetic film F2 through thetunnel barrier TB and the magnetic film F1 without being reflected.

When the applied voltage between the nonmagnetic film N2 and themultilayered film MLF exceeds the height of the Schottky barrier betweenthe magnetic film F2 and the semiconductor film SEM, some down-spinelectrons reaching the magnetic film F2 flow into the semiconductor filmSEM. The electrons once flowing into the semiconductor film SEM cannotreturn to the multilayered film MLF due to a junction electric field,loosing the energy in the semiconductor film SEM and forming a collectorcurrent.

When the nonmagnetic film N2 serving as an electron injecting source andthe multilayered film MLF are connected via a tunnel junction, theenergy of injected electrons (hot electrons) can be freely changed. Forexample, as shown in FIGS. 3 and 4, the state densities of electrons ofFe and Co as representative ferromagnetic substances have sharp peakshigher by approximately 1.5 eV and approximately 1.2 eV, respectively,than the respective Fermi levels. Therefore, by the use of a tunneljunction, it is possible to selectively inject, from the nonmagneticfilm N2, electrons with a specific energy meeting the peak of the statedensity of electrons in the magnetic film F1 or F2. The result is ahigher sensitivity than when, e.g., electrons are injected via aSchottky junction.

FIG. 5 is a view conceptually showing a magnetic device according to anembodiment of the present invention.

The magnetic device shown in FIG. 5 is a three-terminal device differentfrom a common two-terminal device using a magnetoresistance effect. Thisdevice has an emitter (electron injecting section) 10, a base 20, and acollector (electron collecting section) 30. The base 20 is constructedof a multilayered film (to be referred to as a magnetic multilayeredfilm hereinafter) 23 consisting of a magnetic film 21a, a nonmagneticfilm 22, and a magnetic film 21b. The emitter 10 is constructed of anonmagnetic metal film 12 connected to the magnetic multilayered film 23in the base 20 via a tunnel junction member 40. The emitter 20 injectselectrons into the base 20 through the tunnel junction. The tunneljunction member 40 is made of a tunnel insulating film 11. The collector30 is made of a semiconductor layer 31 which forms a Schottky junctiontogether with the magnetic multilayered film 23 in the base 20. That is,on the semiconductor layer 31 serving as the collector 30, the magneticmultilayered film 23 which forms a Schottky junction together with thesemiconductor layer 31 is formed. This magnetic multilayered film 23constitutes the base 20.

In the magnetic multilayered film 23 forming the base 20, ferromagneticfilms such as Co films, CoFe films, or NiFe films are used as themagnetic films 21a and 21b. A nonmagnetic metal film such as a Cu filmor an Ag film is used as the nonmagnetic film 22. That is, the magneticmultilayered film 23 is a three-layered film, known as a spin valvefilm, consisting of a Co/Cu(Ag)/Co or CoFe/Cu(Ag)/CoFe structure.

The magnetic multilayered film 23 is not limited to the three-layeredstructure described above. For example, a magnetic scattering effect canbe enhanced by the use of a multilayered film formed by alternatelystacking large numbers of the magnetic films 21a and 21b and thenonmagnetic films 22. It is also possible to add another metal film toone or both sides of the magnetic multilayered film 23 in order toimprove the Schottky characteristic or the tunnel characteristic. Asemiconductor film or a tunnel insulating film can also be formedbetween the magnetic films 21a and 21b.

Furthermore, the coercive forces of the magnetic films 21a and 21b canbe so set as to be different from each other in order that themagnetization direction in one of the magnetic films 21a and 21b isfixed and only the magnetization direction in the other is changed by anexternal magnetic field. The coercive forces of the magnetic films 21aand 21b can be made different by fixing the magnetization direction inone of the magnetic films 21a and 21b by forming an antiferromagneticfilm adjacent to the film. That is, setting the coercive forces of themagnetic films involves setting them by using an exchange interactionbetween one magnetic film and an adjacent film such as anantiferromagnetic film.

The tunnel insulating film 11 constituting the tunnel junction member 40is formed on the base 20 constructed of the magnetic multilayered film23. The nonmagnetic metal film 12 serving as the emitter 10 is formedvia this tunnel insulating film 11. The base 20 constructed of themagnetic multilayered film 23 and the emitter 10 constructed of thenonmagnetic metal film 12 form a tunnel junction via the tunnelinsulating film 11. Hot electrons are injected from the emitter 10 intothe base 20 through this tunnel junction.

The magnetic device described above has, for example, a practical devicestructure as shown in FIG. 6. That is, on the semiconductor layer 31serving as the collector, the magnetic multilayered film 23 consistingof the magnetic film, the nonmagnetic film, and the magnetic film isformed as the base. The semiconductor layer as the collector and themagnetic multilayered film 23 as the base, except for a device region,are insulated by an insulating interlayer 41. The semiconductor layer 31and the magnetic multilayered film 23 can stably form a Schottkyjunction by interposing a gold layer (not shown). Stabler Schottkycharacteristics can be expected when a metal silicide layer such as anNiSi₂ layer or a CoSi₂ layer is interposed instead of the gold layer.

The tunnel insulating film 11 made of, e.g., an aluminum oxide film, isformed on the magnetic multilayered film 23 as the base. The nonmagneticmetal film 12 such as an aluminum film is formed as the emitter via thetunnel insulating film 11. To improve the tunnel characteristics betweenthe emitter and the base, it is preferable to previously form analuminum film on the magnetic multilayered film 23 as the base, therebyforming a multilayered structure of, e.g., Al/AlOx/Al. The magneticmultilayered film 23 as the base and the nonmagnetic metal film 12 asthe emitter, except a device region, are insulated by an insulatinginterlayer 42.

As shown in FIG. 5, the magnetic device of this embodiment is used as,e.g., a magnetic sensor, by connecting a DC power supply E to theemitter 10 and first and second ammeters A1 and A2 to the base 20 andthe collector 30, respectively. The first ammeter A1 can be connected toeither the magnetic film or the nonmagnetic film of the magneticmultilayered film 23 as the base.

In the above magnetic device, when a voltage V is applied between thebase and the emitter from the DC power supply E, hot electrons areinjected from the emitter 10 into the base 20. If the thickness of thebase 20 is much smaller than the inelastic scattering length of anelectron, these hot electrons reach the base/collector interface withoutloosing energy. If the injection voltage is lower than the height of theSchottky barrier between the base and the collector, the hot electronscannot enter the collector 30. The hot electrons flow out from the base20, and the current value is read by the first ammeter A1.

If the injection voltage exceeds the height of the Schottky barrier,some hot electrons flow into the collector 30. These hot electrons onceflowing into the collector 30 cannot return to the base 20 due to thejunction electric field. The hot electrons lose energy in the collector30 and flow out from the collector 30 through the second ammeter A2.

When the base 20 is formed by the magnetic multilayered film 23 asdescribed above, the probability that hot electrons injected into thebase 20 reach the base/collector interface strongly depends upon thedirections of magnetization in the two magnetic films 21a and 21bconstituting the magnetic multilayered film 23. That is, if themagnetization directions in the two magnetic films 21a and 21b are thesame, the hot electrons can reach the collector 30 without beinginfluenced by spin scattering. However, if the magnetization directionsin the two magnetic films 21a and 21b are opposite, most of the hotelectrons cannot reach the collector 30 under the influence of strongspin scattering and flow out from the base 20 through the first ammeterA1. This phenomenon can be explained by using a theory analogous to thetheory of a common giant magnetoresistance effect pertaining toconduction electrons described earlier with reference to FIGS. 1A to 2B.

As in the case of common spin valve, the directions of magnetization inthe two magnetic films 21a and 21b of the magnetic multilayered film 23can be controlled by properly selecting the thickness of the nonmagneticfilm 22, such that the magnetization directions are antiparallel to eachother when an external magnetic field is zero and parallel to each otherin the presence of an external magnetic field. When the externalmagnetic field is zero, therefore, most of the hot electrons injectedinto the base 20 cannot reach the collector portion 30 and flow out fromthe base 20 through the first ammeter A1. When the external magneticfield is applied, the hot electrons injected into the base 20 flow outprimarily from the collector 30 through the second ammeter A2. In thepresent invention, however, while the antiferromagnetic film describedabove is formed, it is also possible to control the magnetizationdirections in the two magnetic films 21a and 21b such that thedirections are parallel or antiparallel to each other when the externalmagnetic field is zero.

When n-type silicon, for example, is used as the semiconductor layer 31constituting the collector 30, the height of the Schottky barrier formedbetween the semiconductor and a common metal is about 0.5 to 1.0 V.Accordingly, when the device is operated with a bias voltage of 1 V orhigher applied between the base and the emitter, the collector currentis modulated by the external magnetic field. That is, the device can befunctioned as a magnetic sensor by measuring the collector current withthe second ammeter A2. This magnetic sensor can be used as a readmagnetic head of a magnetic recording apparatus.

In principle, the collector current can be modulated by the externalmagnetic field even when a tunnel junction is formed, instead of theSchottky barrier, between the base 20 and the collector 30 by using,e.g., a metal film. If the tunnel junction is formed, however, hotelectrons reaching the base/collector interface do not flow into thecollector 30 easily and there is the possibility that these electronsflow out from the base 20 through the first ammeter A1. To avoid thisproblem, it is necessary to apply a very high bias voltage. In thepresent invention, therefore, it is more effective to form a Schottkybarrier between the base 20 and the collector 30.

Unlike a common spin valve magnetic head, the above magnetic device usesspin scattering of electrons vertically flowing through the magneticmultilayered film 23. Therefore, a higher sensitivity can be obtained inprinciple. Additionally, while a spin valve magnetic head uses amagnetoresistance effect, i.e., spin scattering of conduction electronsexisting near the Fermi level, the magnetic device of the presentinvention uses hot electrons whose energy can be freely controlled by abias voltage and a tunnel junction. Consequently, a larger spinscattering effect can be used.

For example, when the magnetic multilayered film 23 is formed by using amagnetic material having a state density schematically shown in FIG. 7,the state density of an up spin near a Fermi level E_(F) is severaltimes as high as the state density of a down spin, at most. However, fora hot electron having energy E1 much higher than the Fermi level shownin FIG. 7, the state density of a down spin is almost zero and so anextremely strong spin scattering effect can be expected. This is alsotrue of a hot hole having energy E2.

Furthermore, in the above magnetic device, the applied voltage issupported by the tunnel insulating film 23 between the base and theemitter. Therefore, it is readily possible to obtain an appropriatecurrent value under a desired bias voltage by controlling the thicknessof the tunnel insulating film 23. This prevents electromigration,generation of heat, and formation of a magnetic field by a current,which have been problems in the conventional spin valve magnetic heads.Also, the collector 30 behaves as an ideal constant-current source dueto a high junction resistance of the Schottky barrier. This allows avery simple circuit to be used as the second ammeter A2. That is, anoutput can be extracted very easily from this magnetic device.

Example 1!

An example of practical fabrication of the magnetic device shown inFIGS. 5 and 6 and the characteristics of the device will be describedbelow. A practical device structure is as illustrated in FIG. 6.

An n-type silicon layer doped with 10¹⁶ cm³ of boron was used as asemiconductor layer 31 forming a collector 30, and a magneticmultilayered film 23 of Co/Ag/Co was used as a base 20. In this magneticmultilayered film 23, the thickness of each Co film was 3 nm and thethickness of the Ag film was 2 nm. It was confirmed by magnetizationmeasurements that the directions of magnetization in the two Co filmswere antiparallel when an external magnetic field was zero and parallelunder a magnetic field of 100 G or more.

A Schottky junction between the base and the collector was formed byremoving a natural oxide film from the surface of the n-type siliconlayer by using hydrofluoric acid and interposing a 3-nm thick Au film.This Au layer was interposed to form a good Schottky junction with asmall leak. An ohmic contact to a collector terminal was formed byforming an AuSb alloy by vacuum evaporation and heating the alloy.

A 20-nm thick aluminum film was used as a nonmagnetic metal film 12 asan emitter 10, and a 1.5-nm thick aluminum oxide film was used as atunnel insulating film 11. By interposing a 3-nm thick aluminum filmnear the base, a tunnel junction consisting of Al/AlOx/Al was formedbetween the emitter and the base. A silicon thermal oxide film was usedas an insulating interlayer 41 between the collector and the base, andSiO was used as an insulating interlayer 42 between the base and theemitter.

FIG. 8 shows the tunnel characteristic between the emitter and the baseof the above magnetic device, and FIG. 9 shows the Schottkycharacteristic between the base and the collector of the device. FIG. 10shows the result when a collector current IC was measured while avoltage V between the emitter and the base was increased. In FIG. 10, aline La indicates the result when an external magnetic field was zero,and a line Lb indicates the result when a magnetic field of 100 G wasapplied parallel to the magnetic multilayered film 23.

As indicated by the line La in FIG. 10, when an external magnetic fieldwas zero, the collector current IC was very small and most of theelectrons injected into the emitter 10 flowed out from the base 20without reaching the collector 30. When an external magnetic field wasapplied, as indicated by the line Lb, the collector current IC startedflowing when a bias voltage exceeded the voltage of a Schottky barrier(up to 0.8 V). A magnetic field of 100 G was turned on and off while thevoltage between the emitter and the base was fixed at 1.5 V. The resultwas that, as shown in FIG. 11, a large modulation of the collectorcurrent IC was observed, i.e., the magnetic device was found to functionas a magnetic sensor.

FIG. 12 is a view conceptually showing the structure of a magneticdevice according to another embodiment of the present invention. Themagnetic device in FIG. 12 uses a multilayered film 15 consisting of aferromagnetic film 13 and an antiferromagnetic film 14 as an emitter 10.In the magnetic device with this structure, the direction ofmagnetization in the ferromagnetic film 13 in the emitter is fixed bythe exchange interaction between the ferromagnetic film 13 and theantiferromagnetic film 14. Accordingly, the direction of spins of hotelectrons injected from the emitter 10 into a base 20 is held constant.Consequently, the magnitude of a tunnel current flowing from the emitter10 into the base 20 changes in accordance with the magnetizationdirections in magnetic films 21a and 21b of a magnetic multilayered film23. With this structure, it is possible to improve the external magneticfield sensing characteristics.

The magnetic device with the structure shown in FIG. 12 can also berealized by forming the emitter 10 by using a single-layer ferromagneticfilm with a large coercive force, instead of the multilayered film 15consisting of the ferromagnetic film 13 and the antiferromagnetic film14. Furthermore, in the magnetic device with the above structure, themagnetic multilayered film 23 in the base 20 can be replaced with asingle-layer magnetic film as will be described later. Even in thisstructure, the presence/absence of an external magnetic field can bewell sensed. In this structure, a tunnel junction can also be formed byusing a semiconductor film in place of the tunnel insulating film 11.

It was found by experiments analogous to those in Example 1 that themagnetic device shown in FIG. 12 functioned as a magnetic sensor.

FIG. 13 is a view conceptually showing the structure of a magneticdevice according to still another embodiment of the present invention.

In the magnetic device shown in FIG. 13, a semiconductor layer 16similar to a collector 30 is used instead of the metal film formed via atunnel junction to constitute the emitter 10 in the magnetic device inFIG. 5. That is, an emitter 10 and a base 20 form a second Schottkyjunction. This magnetic device has a bipolar transistor structure usinga metal as the base.

In the magnetic device shown in FIG. 13, injection of electrons from theemitter 10 to the base 20 is done by a thermal process via the Schottkyjunction, rather than a tunnel process. The rest of the principle isidentical with that of the magnetic device shown in FIG. 5. In themagnetic device with this structure, as in the magnetic device in FIG.5, a high sensitivity can be obtained and an appropriate current valuecan be readily obtained under a desired bias voltage. This preventselectromigration, generation of heat, and formation of a magnetic fieldby a current, which have been problems in the conventional spin valvemagnetic heads.

In this device in which the emitter 10 is formed by the Schottkyjunction, however, in comparison with the magnetic device shown in FIG.5, the injection voltage cannot be sufficiently raised and so thecollector current tends to decrease compared to the injection current.This is so because the transmittance of a hot electron in thebase/collector interface greatly depends upon its energy. Also, it isnecessary to well control the film formation conditions, the filmstructures, and the like in order to well form the two Schottkyjunctions. In view of these respects, therefore, a more preferredembodiment of the present invention is a magnetic device in whichelectrons are injected through a tunnel junction as described above.

In the magnetic device shown in FIG. 13, it is also possible to excitespin-polarized electrons by irradiating polarized light onto thesemiconductor layer 16 as the emitter 10 and inject the excitedelectrons as hot electrons into the base 20. In the device with thisstructure, a direct transition type semiconductor represented by acompound semiconductor such as GaAs, GaAlAs, CdSe, or CdTe or acaracopalite semiconductor such as CdSiAs₂ is used as the semiconductorlayer 16. When circularly polarized light is irradiated onto such adirect transition type semiconductor, spin-polarized electrons having apolarity based on the direction of polarization of the circularlypolarized light are excited. This semiconductor in which spin-polarizedelectrons are thus excited can function as the emitter 10 for injectingspin-polarized electrons, like the emitter 10 using the ferromagneticfilm in the magnetic device shown in FIG. 12. Accordingly, thisstructure has an advantage in that the external magnetic field sensingcharacteristics are improved as in the case of the magnetic device inFIG. 12. In this structure, as in the above structure, the magneticmultilayered film 23 in the base 20 can be replaced with a single-layermagnetic film.

It was found by experiments similar to those in Example 1 that themagnetic device shown in FIG. 13 functioned as a magnetic sensor.

FIG. 14 is a view conceptually showing the structure of a magneticdevice according to still another embodiment of the present invention.

A base 20 of this device is made of a multilayered film 63 consisting ofa nonmagnetic film 61 and a magnetic film 62. An emitter 10 is made of amagnetic film 52 connected to the nonmagnetic film 61 of the base 20 viaa tunnel junction member 40. The emitter 20 injects hot electrons intothe base 20 through the tunnel junction. The tunnel junction member 40is constructed of a tunnel insulating film 11. A collector (electroncollecting section) 30 is constructed of a semiconductor layer 31 whichforms a Schottky junction together with the magnetic film 62 of the base20.

A magnetic material which is very strong, i.e., has a high coerciveforce, is used as the material of the magnetic film 52, and thereby themagnetization direction in the film is fixed. On the other hand, themagnetic film 62 has a low coercive force and so the magnetizationdirection in the film can be reversed by an external magnetic field.Consequently, the passage of electrons can be controlled as in thedevice shown in FIG. 5. The same effect can be obtained by lowering thecoercive force of the magnetic film 52 and raising the coercive force inthe magnetic film 62 so that only the magnetization direction in themagnetic film 52 can be reversed.

The magnetic device shown in FIG. 14 has, for example, a practicaldevice structure as shown in FIG. 18. That is, on the semiconductorlayer 31 serving as the collector, the multilayered film 63 consistingof the nonmagnetic film 61 and the magnetic film 62 is formed as thebase. The semiconductor layer 31 as the collector and the multilayeredfilm 63 as the base, except for a device region, are insulated by aninsulating interlayer 41. On the multilayered film 63 as the base, thetunnel insulating film 11 constituting the tunnel junction member 40 isformed. The magnetic film 52 serving as the emitter (electron injectingsection) is formed via this tunnel insulating film 11.

The semiconductor layer 31 and the multilayered film 63 can be stablySchottky-junctioned by interposing a gold layer (not shown). StablerSchottky characteristics can be expected by interposing a metal silicidelayer such as an NiSi₂ or CoSi₂ layer instead of the gold layer.

The magnetic device shown in FIG. 14 can be used as, e.g., a magneticsensor, by connecting a DC power supply E to the emitter 10 and firstand second ammeters A1 and A2 to the base 20 and the collector 30,respectively. The first ammeter A1 can be connected to either themagnetic film or the nonmagnetic film of the magnetic multilayered film63 as the base. The collector current is modulated when themagnetization direction in the magnetic film 62 is changed by anexternal magnetic field while a bias voltage higher than the Schottkybarrier is applied between the base and the emitter. That is, the devicecan be function as a magnetic sensor by measuring the collector currentwith the second ammeter A2. This magnetic sensor can be used as, e.g., aread magnetic head of a magnetic recording apparatus.

In the device shown in FIG. 14, the thickness of the base 20 can be madesmaller than in the device shown in FIG. 5, since the number of films inthe base 20 is smaller. Also, since the number of interfaces in the base20 decreases, scattering independent of the direction of a spindecreases. This increases the hot-electron current and consequently thecollector current and thereby improves the device characteristics. Forthese reasons, characteristics superior to those of the device shown inFIG. 5 can be expected from the device shown in FIG. 14.

FIG. 15 is a view conceptually showing the structure of a magneticdevice according to still another embodiment of the present invention.

In this device, a multilayered film 55 consisting of a ferromagneticfilm 53 and an antiferromagnetic film 54 is used as an emitter 10. Thedirection of magnetization in the ferromagnetic film 53 in the emitter10 is fixed by an exchange interaction between the ferromagnetic film 53and the antiferromagnetic film 54. Accordingly, the direction of spinsof hot electrons injected from the emitter 10 into a base 20 is heldconstant. Consequently, the magnitude of a tunnel current from theemitter 10 to the base 20 changes in accordance with the direction ofmagnetization in a magnetic film 62 of a multilayered film 63, i.e., inaccordance with an external magnetic field. With this structure, it ispossible to improve the external magnetic field sensing characteristics.

In the devices shown in FIGS. 14 and 15, a nonmagnetic film 56 can alsobe stacked in the emitter 10 as shown in FIGS. 16 and 17.

In the embodiments shown in FIGS. 14 to 17, a ferromagnetic film such asan Fe film, a Co film, a CoFe film, or an NiFe film is used as themagnetic films 52, 53, and 62. A nonmagnetic metal film such as an Alfilm, a Cu film, or an Ag film is used as the nonmagnetic films 56 and61. As the antiferromagnetic film 54, an FeMn film is used. An exampleof the tunnel insulating film 11 is an AlOx film. An example of thesemiconductor layer 31 is an Si Substrate.

EXAMPLE 2!

An example of practical fabrication of the magnetic devices shown inFIGS. 14 and 18 and the characteristics of the devices will be describedbelow. A practical device structure is as shown in FIG. 18.

As in Example 1, an n-type silicon layer doped with 10¹⁶ /cm³ of boronwas used as a semiconductor layer 31 forming a collector 30, and amultilayered film 63 consisting of an Al nonmagnetic film 61 and an Femagnetic film 62 was used as a base 20. The thickness of the Fe magneticfilm 62 was 2 nm, and the thickness of the Al nonmagnetic film 61 was 5nm. A thermal silicon oxide film was used as an insulating interlayer 41between the collector and the base. A 3-nm thick Au film was interposedbetween the base and the collector to improve the Schottky junctioncharacteristic.

A magnetic film 52 serving as an emitter 10 and made of a CoFe alloy wasstacked on the Al film 61 of the multilayered film 63 via the AlOxtunnel insulating film 11. The AlOx tunnel insulating film 11 was formedby oxidizing the surface of the Al film 61 in an oxygen stream. The CoFemagnetic film 52 was formed by performing sputtering in a magnetic fieldof 1 tesla, and the magnetization direction was fixed.

In the device formed as above, a magnetic field of 100 G was turned onand off at 100 Hz while the voltage between the emitter and the base wasfixed to 1.5 V. Consequently, a large degree of modulation of thecollector current was observed as shown in FIG. 19. The modulation widthwas larger than that in the device of Example 1, i.e., better devicecharacteristics were obtained.

It was confirmed by experiments similar to those in Example 2 that eachof the magnetic devices shown in FIGS. 15 to 17 functioned as a goodmagnetic sensor.

An embodiment using a resonant tunnel junction as a tunnel junctionmember for controlling injection of electrons between an emitter 10 anda base 20 will be described below.

Recently, quantum effect devices have drawn attention and a resonanttunnel device is known as a quantum effect device already found tooperate at room temperature (Richard A. Kiehland, T. C. L. GerhardSollner, High Speed Heterostructure Devices, Semiconductors andSemimetals 41). As a resonant tunnel diode, many experiments andtheoretical calculations have been made for a device using asemiconductor heterojunction as shown in FIG. 20. A resonant tunneldiode with the structure as shown in FIG. 20 is particularly called adouble barrier resonant tunnel diode in which an AlGaAs regioncorresponds to a barrier portion. It is well known that a resonanttunnel phenomenon occurs regardless of the number of barriers.

FIG. 21 shows a change in the anode current as a function of a change inthe cathode voltage (H. Ohnishi et. al., Appl. Phys. Lett. 49 (1986),1248). FIG. 21 shows that a sharp peak is found at a specific voltage inthe current-voltage characteristic. This phenomenon is known as aresonant tunnel phenomenon. This is understood as a phenomenon in whichwhen the resonance level in a region called a quantum well sandwichedbetween barriers agrees with the Fermi level of the cathode, the tunnelprobability of an electron becomes 1and the tunnel resistance of theelectron decreases. A resonant tunnel diode shows a negativedifferential current-voltage characteristic as shown in FIG. 21 and hasa very high sensitivity.

When a magnetic field is applied to this double barrier tunnel diodeusing a semiconductor heterojunction, a Zeeman effect occurs and theresonance level in the quantum well splits in accordance with the spinsof electrons. Therefore, the peak position in the current-voltagecharacteristic changes in accordance with the difference between thestates (up or down) of spins of electrons injected from the cathode. Byusing this phenomenon, the spin state of electrons on the cathode sidecan be known by measuring the peak position of the anode current.

Although experiments have been primarily made on resonant tunnel devicesusing a semiconductor heterojunction, the phenomenon is independent ofthe material, provided that a device has the structure shown in FIG. 20.However, many experiments have been made in semiconductors because theresonant tunnel phenomenon is conspicuously seen when scattering of,e.g., phonons in the quantum well is little and the electron density islow. Therefore, the resonant tunnel phenomenon is also seen in aresonant tunnel diode using a metal/insulator heterojunction or ametal/semiconductor heterojunction. Recently, experiments made onresonant tunnel diodes using these systems are also reported.

The band discontinuity in a metal/insulator, e.g., (CoSi₂)/(CaF₂),heterojunction is as large as 15 eV, 60 times or more larger than 0.25eV as the band discontinuity in an AlGaAs/GaAs semiconductorheterojunction. A double barrier tunnel diode can be effectuated byusing CaF₂ and CoSi₂ as the barrier and the quantum well, respectively,in the structure shown in FIG. 20. Since the band discontinuity islarge, the tunnel probability of electrons injected from the cathode islow. Therefore, it is necessary to decrease the thicknesses of thebarrier and the quantum well layer. However, the resonant tunnelphenomenon can be expected when the barrier layer is 0.9 nm and thequantum well layer is 1.9 nm.

Also, unlike a semiconductor heterojunction, for a metal/insulatorheterojunction, there is a technique of controlling a layer of severalmolecules, and so a resonant tunnel diode of this sort can be realized.In effect, a triple barrier resonant tunnel diode using this CaF₂ /CoSi₂heterojunction was found to have a negative differential resistancecharacteristic at room temperature (T. Suemasu et. al., Electron Lett.28, 1432 (1992)). A resonant tunnel diode using a metal/semiconductor,e.g., (NiAl)/ (AlAs), heterojunction was also found to have a negativedifferential resistance characteristic (N. Tabatabaie et. al., Appl.Phys. Lett., 53, 2528 (1988)).

For the reasons explained above, another metal/insulator heterojunctioncan be realized. For example, a metal/insulator, e.g., (Fe)/(Al₂ O₃),heterojunction can be formed by using Fe as a metal, growing Al on Fe,and oxidizing Al. This heterojunction has a band discontinuity of about15 eV. A resonant tunnel diode can be realized by controlling the filmthickness of this heterojunction to be substantially equal to the filmthickness of a CaF₂ /CoSi₂ heterojunction.

Furthermore, when a ferromagnetic substance such as Fe is thus used as aquantum well, a molecular field produces an energy level difference ofabout 1 eV between up-spin electrons and down-spin electrons.Consequently, the resonance level in the quantum well splits inaccordance with whether electrons are up-spin electrons or down-spinelectrons. Accordingly, the peak position in the current-voltagecharacteristic changes in accordance with the spin state of electronsinjected from the cathode. Consequently, the spin state of electrons onthe cathode side can be known.

Unlike a semiconductor heterojunction resonant tunnel diode, in aresonant tunnel diode using such a ferromagnetic substance, the spinstate of electrons in the cathode can be known without externallyapplying any high magnetic field. It is also possible to use an Fe/ZnSeheterojunction as a metal/semiconductor heterojunction. Furthermore, asemimetal such as graphite can be used in the barrier portion. Inparticular, graphite facilitates formation of the barrier portion sincegraphite has no vertical state to the surface and hence behaves like aninsulator and at the same time allows an easy control of each molecularlayer.

A resonant tunnel junction can be used as the tunnel junction member inany of the embodiments described with reference to FIGS. 1A to 19. As anexample, FIG. 22 conceptually shows a structure using the resonanttunnel junction in the magnetic device shown in FIG. 5. The samereference numerals as in FIG. 5 denote the same parts in FIG. 22 and adetailed description thereof will be omitted unless it is necessary.

This magnetic device has an emitter (electron injecting section) 10, abase 20, and a collector (electron collecting section) 30. A doublebarrier resonant tunnel diode is used as a tunnel junction member 70between the emitter and the base. The tunnel junction member 70 consistsof a semiconductor barrier layer 71 as one barrier positioned near theemitter 10, a semiconductor quantum well layer 72 equivalent to aquantum well, and a semiconductor barrier layer 73 as the other barriernear the base 20. As the resonant tunnel diode used in the tunneljunction member 70, the metal/insulator heterojunction or themetal/semiconductor resonant tunnel diode described above can also beused in place of the semiconductor heterojunction resonant tunnel diode.Also, instead of the double barrier resonant tunnel diode, a triplebarrier resonant tunnel diode or a resonant tunnel diode having abarrier of higher order can be used.

In the tunnel junction member 70, the resonance level of the resonanttunnel diode must be higher than the height of the Schottky barrierbetween the base and the collector. This resonance level can beappropriately set by properly selecting the material of the resonanttunnel diode and the thickness of the quantum well. Also, to improve thesensitivity of the collector current to the injection voltage of theresonant tunnel device, the height of the barrier between the base andthe collector can be adjusted by inverting the voltage between the baseand the collector.

In the magnetic device shown in FIG. 22, the resonant tunnel device isused in the tunnel junction member 70. This resonant tunnel deviceinsulates a metal film 12 in the emitter 10 from a magnetic multilayeredfilm 23 in the base 20 and allows injection of hot electrons into themagnetic multilayered film 23 with a tunnel probability of 1 withrespect to an emitter voltage comparable to the peak voltage. That is,the energy of hot electrons injected from the emitter is chosen by thetunnel probability, and this makes injection of electrons with a narrowenergy width feasible. Since, therefore, this selects the energy ofelectrons to be injected, the smaller the energy width of electrons tobe injected, the higher the expected sensitivity, when a magneticmaterial having a state density as shown in FIG. 7 is taken intoconsideration. Furthermore, the line width of the resonance level isdecreased when a material such as a metal/insulator heterojunctionresonant tunnel diode having a large band discontinuity is used.Accordingly, in this case, a magnetoresistance effect with a highersensitivity can be expected.

The absolute value of a current density can be adjusted by adjusting themagnitude of the current density by interposing a thin insulating filmbetween the metal film 12 in the emitter 10 and the tunnel junctionmember 70. The absolute value of the current density can also beadjusted by adjusting the thickness of the barrier of the resonanttunnel diode in the tunnel junction member 70.

EXAMPLE 3!

In a structure shown in FIG. 20, 10¹⁶ cm⁻³ doped n-type silicon was usedas a semiconductor layer 31 in a collector 30. A magnetic multilayeredfilm 23 in a base 20 has a Co/Ag/Co structure in which the thicknessesof the Co layer and the Ag layer were 3 nm and 20 nm, respectively. A20-nm thick Al nonmagnetic metal film was used in an emitter 10. Thismagnetic multilayered structure is also known as a GMR structure.

The height of the Schottky barrier between the n-type silicon in thecollector 30 and the magnetic multilayered film 23 was about 0.8 eV.When a voltage of 0.8 V or higher was applied between the emitter andthe base, the collector current abruptly rose. When the emitter/basevoltage was set to 3 V and the input current from the emitter to thebase was set to 2 mA by adjusting a tunnel junction member 70, thecollector current was very low (0.2 mA or less) due to spin scatteringin a zero magnetic field. When a magnetic field of 100 G or higher wasapplied, spins in the magnetic film in the multilayered film 23 werepointed in the same direction, and a collector current of 1.2 mA couldbe extracted.

As the tunnel junction member 70, a double barrier resonant tunneltransistor having an Al₂ O₃ layer 71/Fe layer 72/Al₂ O₃ layer 73heterojunction was used. When the thickness of each of the Al₂ O₃ layers71 and 73 as barriers was 0.5 nm and the thickness of the Feferromagnetic layer 73 as a quantum well was 3 nm, a current of 10 mAwas obtained with 1.7 V at room temperature.

EXAMPLE 4!

A structure show in FIG. 22 was formed under the same conditions as inExample 3 except for a tunnel junction member 70. As the tunnel junctionmember 70, a double barrier resonant tunnel transistor having a CaF₂layer 71/CoSi₂ layer 72/CaF₂ layer 73 heterojunction was used. When thethickness of each of the CaF₂ layers 71 and 73 as barriers was 0.5 nmand the thickness of the CoSi₂ ferromagnetic layer 72 as a quantum wellwas 3 nm, a current of 10 mA was obtained with 1.7 V at roomtemperature.

FIG. 23 is a view conceptually showing a magnetic material device usinga resonant tunnel structure according to still another embodiment of thepresent invention.

In this embodiment, a resonant tunnel multilayered film 80 and a metalfilm 85 are formed as a base 20 between a metal film 86 as an emitter 10and a semiconductor layer 81 as a collector 30. The resonant tunnelmultilayered film 80 consists of an insulating film 81, a magnetic film82, and an insulating film 83.

In FIG. 23, the multilayered film 80 constitutes a double barrierresonant tunnel diode. However, this resonant tunnel diode can have anynumber of layers. Also, the insulating films 81 and 83 can besemiconductor films. The metal film 85 between the multilayered film 80and the semiconductor layer 31 is a layer for allowing the multilayeredfilm 80 as a resonant tunnel device to stably operate. A base electrodeis formed from this layer. A Schottky junction is formed between themetal film 85 and the semiconductor layer 31 as the collector 30. Hotelectrons having an energy higher than this Schottky barrier areinjected from the metal film 86 as the emitter 10.

When the metal films 85 and 86 are made of the same material, an idealdouble barrier tunnel transistor can be formed. The metal films 85 and86 are formed by using a soft magnetic material (a magnetic materialwith a low coercive force) 89 such as soft iron so as to be readilymagnetized with a weak magnetic field. Consequently, the metal film 86in the emitter 10 is uniformly magnetized in the same direction by aslight magnetic field output from a recording medium, and electronsinjected from the emitter are spun in a fixed direction. The magneticfilm 82 in the multilayered film 80 is made of a hard magnetic material(a magnetic material with a high coercive force) such as a CoFe alloy sothat the direction of magnetization does not change easily due to anexternal magnetic field. If the thickness of the multilayered film 80 asa double barrier tunnel diode is much smaller than the inelasticscattering length, electrons can reach the collector 30 without loosingthe state of spins which the electrons took in the metal film 86.

When n-type silicon is used as the semiconductor layer 31 in thecollector 30, the height of the Schottky barrier formed between thissilicon and a common metal is approximately 0.5 to 1.0 eV. Therefore, avoltage of 1 V or higher exceeding this height is applied between theemitter and the base to inject electrons. If the voltage between theemitter and the base is 3 V or higher, the inelastic scattering lengthabruptly shortens and this requires the size of the device structure tobe decreased. To hold an inelastic scattering length of about 10 nm,therefore, control is so performed that a resonant tunnel phenomenonoccurs with an emitter-base voltage of about 1 to 3 V. This is readilyaccomplished by adjusting the material and the width of the quantumwell. Furthermore, to improve the sensitivity of the collector currentto the injection voltage of the resonant tunnel device, the barrierbetween the base and the collector can be adjusted by inverting thebase-collector voltage.

Assume, for example, that a magnetic material having a state density asshown in FIG. 7 is used as the quantum well magnetic material 82. Inthis case, for hot electrons equivalent to energy E1, there is no statedensity of down-spin electrons in the quantum well, and the resonancelevel exists only for up-spin electrons. Accordingly, amagnetoresistance effect with a higher sensitivity can be expected byadjusting the thickness of the insulating film 81 in the resonant tunneldevice 80 so that the energy E1 is equivalent to the resonance level.

EXAMPLE 5!

In a structure shown in FIG. 23, a 10¹⁶ cm⁻³ doped n-type silicon wasused as a semiconductor 31 in a collector. A base 20 had a multilayeredstructure of an Al₂ O₃ layer 81, a CoFe layer 82, an A1₂ O₃ layer 83,and an Fe film 85. The thickness of each of the Al₂ O₃ layers 81 and 83was 0.5 nm, and the thickness of each of the quantum well CoFe layer 82and the Fe film 85 was 3 nm. Soft iron was used as a metal film 86 in anemitter 10.

When up-spin hot electrons were injected from the emitter 10, a peakcurrent was obtained at 1.7 V. When down-spin hot electrons wereinjected, the current value was small, not exceeding one-hundredth ofthe peak current. Consequently, it was possible to discriminate the spinstates of electrons in the emitter 10.

The reason for this can be considered that a CoFe alloy has a statedensity as shown in FIG. 7. That is, in a quantum well consisting ofCoFe, for hot electrons exceeding the height of the Schottky barrierbetween the collector 30 and the metal film 85 in the base 20, theresonance level exists for up-spin electrons and there is no resonancelevel for down-spin electrons.

EXAMPLE 6!

A structure shown in FIG. 23 was formed under the same conditions as inExample 5 except for a base 20. The base 20 had a triple barrierresonant tunnel structure consisting of an Al₂ O₃ layer 81, a CoFe layer82, an Al₂ O₃ layer 83, a CoFe layer 82, an Al₂ O₃ layer 83, and an Fefilm 85. The thickness of each of the Al₂ O₃ layers 81 and 83 was 0.5nm, and the thickness of each of the quantum well CoFe layer 82 and theFe film 85 was 3 nm.

When up-spin hot electrons were injected from an emitter 10, a peakcurrent was obtained at 1.2 V. When down-spin hot electrons wereinjected, the current value was small, not exceeding one-hundredth ofthe peak current. Consequently, it was possible to distinguish betweenthe spin states of electrons in the emitter 10.

FIG. 24 is a view conceptually showing a magnetic device using aresonant tunnel structure according to still another embodiment of thepresent invention.

In this embodiment, a resonant tunnel multilayered film 80 consisting ofan insulating film 81, a magnetic film 82, and an insulating film 83 isformed between a metal film 91 serving as a cathode (electron injectingsection) for injecting electrons into the multilayered film 80 and ametal film 92 serving as an anode (electron collecting section) intowhich electrons flow from the multilayered film 80. In FIG. 24, themultilayered film 80 constitutes a double barrier resonant tunnel diode.However, this resonant tunnel diode can have any number of layers.

When the metal films 91 and 92 are made of the same material, an idealdouble barrier tunnel transistor can be formed. The metal films 91 and92 are formed by using a soft magnetic material such as soft iron so asto be readily magnetized with a weak magnetic field. Consequently, themetal film 91 as the cathode is uniformly magnetized in the samedirection by a slight magnetic field output from a recording medium, andelectrons injected from the emitter are spun in a fixed direction. Themagnetic film 82 in the multilayered film 80 is made of a hard magneticmaterial such as a CoFe alloy so that the direction of magnetizationdoes not change easily due to an external magnetic field. If thethickness of the multilayered film 80 as a double barrier tunnel diodeis much smaller than the inelastic scattering length, electrons canreach the collector 30 without loosing the state of spins which theelectrons took in the metal film 91.

In a resonant tunnel diode like this, a resonance level splitcorresponding to a molecular field in the quantum well magnetic film 82occurs, and a shift of the peak corresponding to the split is producedin the current-voltage characteristic by the spin state. Assume, forexample, that a magnetic material having a state density as shown inFIG. 7 is used as the quantum well magnetic film 82. In this case, forhot electrons corresponding to energy El, there is no state density ofdown-spin electrons in the quantum well, and a resonance level existsonly for up-spin electrons. Therefore, a magnetoresistance effect with ahigher sensitivity can be expected when the thickness of the insulatingfilm 81 of the resonant tunnel device 80 is so adjusted that the energyE1 is equivalent to the resonance level.

EXAMPLE 7!

In a structure shown in FIG. 24, a resonant tunnel multilayered film 80was formed to have a triple barrier resonant tunnel structure consistingof an Al₂ O₃ layer 81, a CoFe layer 82, an Al₂ O₃ layer 81, a CoFe layer82, an Al₂ O₃ layer 83, and an Fe layer. The thickness of each of theAl₂ O₃ layers 81 and 83 was 0.5 nm, and the thickness of each of thequantum well CoFe layer 82 and the Fe layer was 3 nm. The thickness ofan Fe film 92 in an anode was 3 nm. Soft iron was used as a metal film91 in a cathode.

When up-spin hot electrons were injected from the cathode, a peakcurrent was obtained at 1.2 V. When down-spin hot electrons wereinjected, the current value was small, not exceeding one-hundredth ofthe peak current. Consequently, it was possible to discriminate the spinstates of electrons in the cathode.

The reason for this can be considered that a CoFe alloy has a statedensity as shown in FIG. 7. That is, in a quantum well consisting ofCoFe, for hot electrons exceeding the height of the Schottky barrierbetween a collector 30 and a metal film 85 in a base 20, the resonancelevel exists for up-spin electrons and there is no resonance level fordown-spin electrons.

In the magnetic device of the present invention as has been describedabove, a high sensitivity can be obtained and stable operatingcharacteristics can be obtained with a low current density, compared toconventional two-terminal devices using a magnetoresistance effect.Also, the magnetic sensor of the present invention using this magneticdevice can sense an external magnetic field stably at a highsensitivity.

Additional advantages and modifications will readily occur to thoseskilled in the art. Therefore, the invention in its broader aspects isnot limited to the specific details, and representative devices shownand described herein. Accordingly, various modifications may be madewithout departing from the spirit or scope of the general inventiveconcept as defined by the appended claims and their equivalents.

What is claimed is:
 1. A magnetic device comprising:a multilayered filmhaving a first magnetic film and a nonmagnetic film; an electroncollecting section including a semiconductor layer connected to saidfirst magnetic film via a Schottky junction; and an electron injectingsection including a second magnetic film connected to said nonmagneticfilm via a tunnel junction member.
 2. A device according to claim 1,wherein said first and second magnetic films are so set as to havedifferent coercive forces.
 3. A device according to claim 1, whereinsaid tunnel junction member comprises a resonant tunnel structureincluding first and second barrier layers and a quantum well layerinterposed between said first and second barrier layers.
 4. A magneticmaterial sensor comprising:a multilayered film including a firstmagnetic film and a nonmagnetic film; an electron collecting sectionincluding a semiconductor layer connected to said first magnetic filmvia a Schottky junction; an electron injecting section including asecond magnetic film connected to said nonmagnetic film via a tunneljunction member; a power supply for applying a voltage to said electroninjecting section; and means for detecting a current flowing out fromsaid electron collecting section, wherein when a relationship betweenmagnetization directions in said first and second magnetic materialfilms is changed by an external magnetic field, the current flowing outfrom said electron collecting section changes accordingly, and theexternal magnetic field is sensed on the basis of the change in thecurrent.
 5. A sensor according to claim 4, wherein said first and secondmagnetic films are so set as to have different coercive forces.
 6. Asensor according to claim 4, wherein said tunnel junction membercomprises a resonant tunnel structure including first and second barrierlayers and a quantum well layer interposed between said first and secondbarrier layers.